


biological imperative

by Anonymous



Category: Voltron: Legendary Defender
Genre: Alien Biology, Dubious Consent, Fuck Or Die, M/M, Plot What Plot/Porn Without Plot
Language: English
Status: Completed
Published: 2018-12-01
Updated: 2018-12-01
Packaged: 2019-09-05 01:37:06
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,155
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16801093
Author URL: https://archiveofourown.org/
Summary: It's just biology,Shiro tells himself for the umpteenth time.It doesn't mean anything.





	biological imperative

**Author's Note:**

> I was clearing out my WIP folder and found this, thought I might bring to to AO3. Originally written for the VLD kink meme for the prompt "Sheith: fuck or die, Galra biology." I wrote this from the perspective that Shiro and Keith are mutually pining, but "fuck or die" tropes are inherently dubcon so please bear that in mind.

“Are you sure about this?” he asks for what feels like the millionth time.

“Are _you?_ ” Keith replies sharply. There’s something defensive about his tone, about the way his body is hunched in on itself. It’s a familiar look, but not one that Shiro has ever seen directed at him.

“Hey,” he says, his tone softening. “Of course I am.” _I’d do anything for you_ , is what he doesn’t say. No point adding the weight of his own emotions to the gravity of the situation. If what Krolia says is true, Keith is going to be out of it pretty soon, and one of them needs to retain a sense of objectivity, a sense of control.

“Okay, well. Good.” He turns away from Shiro and begins undressing with jerky movements, his shoulders still hunched over like he’s trying to keep himself hidden, make himself smaller.

“Keith,” says Shiro, placing a hand on his wrist. Keith flinches but doesn’t pull away. “Keith, just look at me.”

Keith turns, not without some reluctance. Shiro can see a dull flush has begun to set in, from the tops of his cheekbones and down his throat to where it spills over his chest. In the dim light of his quarters, Shiro could swear his irises are almost purple.

“We’re going to get through this the same way we’ve gotten through everything else that’s been thrown our way.” He takes Keith’s hand in his own. “Together,” he finishes, giving it a quick squeeze.

Keith growls low in his throat and before he knows it, Shiro’s being pushed up against the wall, Keith’s hands finding their way under his shirt lightning-fast. Keith’s all over him; mouthing at his jaw, his neck, and the sudden shock of it is enough to force the breath out of him.

“Need you,” he says as he fits his thigh between Shiro’s legs, the pressure too much too soon.

Shiro places his hands on Keith’s shoulders, trying to ground him. “It’s okay, I’m here now. I’m whatever you need me to be.”

Keith growls again and bites Shiro’s lower lip before slotting their mouths together. The kiss is vicious, as if Keith’s pouring all the frustration of the last few weeks into it, and Shiro surrenders to it, lets Keith take what he needs.

“Off,” says Keith once he breaks the kiss, his nails surprisingly sharp as they scrape over Shiro’s abs.

Keith tugs his shirt over his head with such force he’s surprised it doesn’t tear at the seams. Shiro has a brief moment to feel self-conscious, but then Keith is stepping back, looking at him like he wants to _devour_ him, like he doesn’t even see the scars. Shiro’s cheeks colour under his gaze in a way that has little to do with embarrassment.

The moment is broken when Keith lunges for him again. This time it’s skin on skin, and if Shiro’s enjoying how it feels then it’s nothing compared to Keith. His hands are running incessantly over his chest, his back, as if he’s trying to learn Shiro’s body by touch alone. Shiro’s all too aware of the hard line of Keith’s erection pressed against his thigh, and when he grinds against it experimentally Keith groans full-throated, uninhibited.

“Is this what you need?” he asks, because even though it’s obvious, he needs to hear it from Keith.

“ _Yes_ ,” he hisses, burying his face in the crook of Shiro’s neck and chasing more of that friction.

“Okay,” he murmurs, pressing a kiss to Keith’s temple.

Shiro makes quick work of their pants while Keith claws at him helplessly, pressing his mouth to every inch of exposed skin. When they’re both naked, Keith begins to grind against him in earnest and Shiro is quick to realise they’re not going to get anywhere if they carry on like this.

“Bed,” he says, pushing Keith backwards. The whine Keith lets out is nothing short of petulant, and Shiro can’t help but smile at the knowledge that even like this, Keith is as stubborn as ever.

Keith hits the bed first and Shiro only has a moment to admire the way he looks ( _his hair dishevelled, lips full and bitten, cock hard and leaking against his stomach in a way that makes Shiro’s mouth water_ ) before he’s being pulled down on top of him with near-inhuman strength.

“I need—”

“I know,” Shiro says, stroking his face in a way that seems almost too tender for the situation they’re in. But Shiro never could stop himself from blurring the lines where Keith is concerned, and the resultant guilt is all too familiar. _It’s just biology,_ he tells himself for the umpteenth time, _it doesn’t mean anything._ But try as he might, he can’t help the lurch in his stomach when he sees Keith lean into the touch, practically nuzzling his hand.

Keith says his name again and it comes out as a whine, a plea, and Shiro is in no position to deny him anything. “It’s okay, I know what you need. Just let me take the edge off first.”

Keith’s brows crinkle for a moment but when Shiro gets a hand around his erection his mouth falls open with an _oh_ that’s part understanding, part pleasure.

“Is this okay?” he asks again.

Keith doesn’t reply, just seizes Shiro’s face and kisses him deeply, his hips erratically thrusting into the tight ring of Shiro’s fist. Shiro tastes iron and realises his lip is split, surprised by how sharp Keith’s teeth are.

His thoughts are broken by Keith moaning his name again, sounding more desperate than ever. “I—Please, it’s not enough—”

“Okay,” he says, planting a kiss on the corner of Keith’s mouth.

Keith’s eyes are glassy and hooded as they track Shiro’s movements down his body. Selfishly, Shiro finds he wants to map Keith’s body with his mouth, run his tongue over each and every scar, find all the places that make him moan and shake. His own erection hangs heavy between his legs and he wants nothing more than to take them both in hand, to gaze into Keith’s eyes as he sees the exact moment he falls apart.

But this isn’t about Shiro. _You’re here to help Keith,_ he reminds himself. _You’re only here to save his life, because no one else could._

He pauses when he reaches Keith’s dick, hovering over it for a moment, mouth just inches away as he silently asks permission. Maybe it’s a trick of the light but Keith’s eyes seem to be glowing yellow in the dim room, pupils blown with desire. All it takes is Keith gasping out a strangled _please_ before Shiro’s wrapping his lips around the head of his dick, his hand firm around the base.

The effect is instantaneous: Keith’s whole body goes taut, arching off the bed as a high-pitched whine escapes his throat. One of his hands buries itself in Shiro’s hair while the other claws against his jaw, breaking the skin. Shiro does his best to hold him down but Keith’s stronger than Shiro’s ever seen him, and he has to use the strength of his prosthetic arm to keep his hips on the bed.

Shiro wastes no time on teasing or technique, just works on taking Keith as deep as he can. He bobs his head, trying to keep up a rhythm despite Keith doing everything in his power to force himself deeper into the wet heat of his mouth. On an upstroke he chances a glance at Keith who’s completely wrecked, one arm thrown across his eyes as if the combined sensations of seeing and feeling are too overwhelming for him, the other hand uselessly convulsing against the bedsheets. He’s panting, his narrow chest rising and falling with every stuttered inhalation, and Shiro can tell he’s already so close, he just needs something _more_.

Shiro has some idea of what that might be. He removes his hand from the base of Keith’s dick and takes him as far as he can, sinking down until his nose is pressed against his pubic bone. With his free hand, he reaches behind Keith’s balls and presses two fingers against his perineum, rubbing the sensitive area insistently.

And that’s all it takes—suddenly Keith is twisting underneath his grip and shuddering out a breathless moan. His hands lock around the back of Shiro’s head and he can’t help but choke as Keith fucks his face, riding out his orgasm with a series of powerful thrusts down his throat. Tears leak out the corners of Shiro’s eyes as he waits for Keith’s grip to slacken, and by the time he finally pulls off his face is a mess of come and spit.

Keith has collapsed back onto the bed, his eyes wide and unseeing as his whole body is wracked with shaky breaths. Shiro wipes his mouth with the back of his hand and reaches out to touch Keith. His pulse is racing when Shiro presses two fingers to his throat, but Shiro can feel his breaths grow steady with every passing second. He doesn’t respond when Shiro calls his name, but he does nuzzle into Shiro’s touch as he had before, as if his subconscious was hardwired to seek Shiro’s touch.

_It’s just biology._

Shiro knows he has little time to waste. Soon Keith will be alert and insatiable once more, and Shiro intends to be ready. He digs around on the floor for his pants and fishes a bottle of lube out of one of his pockets before returning to the bed. Already Keith’s eyes—still hazy and unfocused—are tracking his movements with a detached interest, and Shiro knows he needs to act fast.

He shifts to a kneeling position and preps himself in a manner that’s both clinical and perfunctory, doing his best to hide any signs of pleasure from showing on his face. The stimulation makes his neglected cock throb and he flushes in embarrassment when his dick begins leak against his thigh. By now Keith’s regarding him intently, his eyes fixed on the place where Shiro’s fingers are disappearing into his body with an obvious hunger.

Shiro has to bite back a moan when he inserts a third finger, the heat rising in his face once more. He doesn’t miss the way Keith’s dick twitches at the sight, already beginning to fill and harden against his stomach.

Shiro removes his fingers and wipes them on the sheets then reaches out to touch Keith’s hip with his clean hand. “Hey,” he says, keeping his voice soft and gentle, “back with me?”

When Keith finally replies his voice is faint and distant. “Yeah,” he says, not taking his eyes off Shiro’s cock. Shiro’s mouth goes dry at the raw desire in his eyes, his own breath coming quickly now. He presses his palm to Keith’s forehead and finds him feverish, and the contact causes Keith’s eyes to guiltily meet his own.

“Keith, you’re burning up. Maybe I should get you a—”

“No,” he says, his voice desperate and broken. He grabs Shiro’s wrist with a bruising strength and holds him fast. “Please don’t leave me.”

Shiro feels a familiar pang of guilt in his chest, an old wound that never quite healed. “Okay,” he says, brushing Keith’s sweaty hair from his forehead. Keith’s eyes flutter closed at the touch and Shiro takes a moment to appreciate how strikingly beautiful he is like this; long eyelashes fanned out against his cheekbones, kiss-bitten lips dark and shiny, post-sex flush still bright on his cheeks. “It’s okay, I’m not going anywhere.”

Keith closes the space between them and kisses him like he’s starved for it, like he never wants to stop touching him. For a brief moment Shiro lets himself get caught up in the fantasy, that the two of them really are lovers and the passion Keith feels for him is genuine.

He shoves that thought away as quickly as it comes. This isn’t about him.

“What do you need?” he murmurs against Keith lips.

“I need—Shiro I—” He bites his lip and looks away.

Shiro gently hooks his fingers under Keith’s jaw, turning his face back towards him. “Keith it’s okay, just tell me. Anything you want, it’s yours.”

Keith eyes darken, causing something to stir in the pit of Shiro’s stomach. He licks his lips. “I want to fuck you.”

“Okay,” he says, placing a chaste kiss on Keith’s lips. Even though he already knew it, it feels good to hear Keith say it out loud, to confirm that he really does want Shiro like this. _Or at least he thinks he does,_ he reminds himself. Keith’s out of his mind right now, all intellect and common sense stripped back to the point where he’s nothing more than his biological urges. _You’re doing this to save him,_ he reminds himself again. _It doesn’t mean anything._

“Shiro,” he says, biting at Shiro’s swollen lower lip. “Need you now.”

Shiro nods and moves down the bed once more. Keith has already taken himself in hand and is fucking his fist with shallow, abortive movements, as if the stimulation is both too much and not enough at the same time. Shiro is momentarily transfixed by the sight of Keith’s dick, shiny with precome, as it slides through his fist.

“Shiro, _please_.”

“Yeah,” he says, running a hand through his hair. Keith removes his hand—not without some reluctance—and Shiro replaces it with his own, giving the base of his dick a gentle squeeze. The groan it elicits is guttural, and Shiro takes some misplaced pride in knowing that he caused Keith to make that sound when his own touch had failed.

Shiro quickly slicks up Keith’s dick and moves to straddle his hips, holding him steady as he rubs the head of his cock over his hole. Keith looks like he’s about to lose it when Shiro finally begins to sink down, working himself open inch by inch. Shiro forces himself to go slow; it’s been a long time since he’s done this and Keith isn’t small by any stretch of the imagination. He really should have spent more time prepping himself, and Shiro’s desperately grateful for whatever thread of self-control Keith’s clinging to that’s preventing him from fucking up into Shiro right away.

Shiro’s more than a little breathless by the time he’s fully seated, panting from exertion. He gives himself a moment to adjust, running his hands up and down Keith’s sides in an attempt to soothe him as he becomes increasingly agitated. It’s clear that he’s fighting an internal battle with himself, wanting to fuck Shiro with abandon but forcing himself to hold back.

Shiro lays a trail of kisses down his sternum and starts moving slowly. The first movement of Keith inside him sparks pleasure deep in his gut, and it’s not long before he falls into a steady rhythm, one hand splayed over Keith’s chest while he works himself on his cock.

“Shiro,” he says urgently, grabbing his hips with enough force to bruise. “Shiro I can’t—I’m trying but I can’t—”

“It’s okay,” he says breathlessly, “you don’t have to hold back. I can take it.” He finds one of Keith’s hands and links their fingers together. “Whatever you have to give me, I can take it.”

Keith growls deep in his throat, his grip on Shiro’s hips becoming excruciating. Without warning, he lifts Shiro off him and flips him onto his back with such force that Shiro finds himself winded. Keith grabs his calves and presses them against his chest, effectively folding him in two. Before Shiro can adjust, Keith’s lining up and pushing in again, setting a brutal pace that has Shiro incoherent, moaning brokenly with every thrust.

“Touch yourself,” Keith says in a voice that’s too deep to be Keith, too deep to be human. And that’s when Shiro notices it.

Keith’s eyes are glowing yellow, a stark contrast against the purple irises. When Keith bites his neck it’s with teeth that are fanged, the canines elongated and sharp. Keith’s holding him still with one hand on his hip and another on his shoulder, and the force of his unyielding grip surpasses anything Keith could exert under normal circumstances. The scratches on his body, he realises, are not from Keith’s nails but from his _claws_.

“Do it,” he orders, bringing Shiro back to himself.

Shiro moans Keith’s name as he complies, summoning what’s left of his coordination to wrap a hand around himself. Any guilt at the thought of enjoying this instantly melts away as Shiro starts jerking himself in earnest, surrendering to sensation of Keith driving into him as his own hand works his cock. Shiro’s orgasm completely blindsides him, his eyes squeezed shut from the intensity of it as he spills messily over his own stomach. For a long time he’s aware of nothing more than the rush of blood in his ears, of Keith’s breath hot on his face as he pants with exertion.

Keith fucks him through it, a relentless pace that has Shiro gasping as he becomes hypersensitive. Keith’s eyes are wide and wild, and he shows no signs of slowing down. But Shiro meant it when he said he’d take anything Keith was willing to give him, and soon the hypersensitivity abates until Shiro is left boneless in a post-orgasm haze. Keith is fucking him with an intensity that’s almost animalistic, and it’s all Shiro can do to hold himself open, to let Keith use him.

“Shiro,” Keith says, and it comes out as a plea. Shiro doesn’t know what Keith’s begging for but he’d do anything to give it to him.

“Keith, it’s okay,” he says breathlessly, “it’s okay Keith. You can let go.”

Keith cries out, a strangled noise that sounds almost like Shiro’s name. He thrusts one final time, burying himself impossibly deep, shocking a moan out of Shiro. He buries his face in the crook of Shiro’s neck, and they stay together like that for what feels like an age; Keith panting into Shiro’s skin while Shiro strokes Keith’s hair.

When Keith gently eases out of Shiro and pulls back, Shiro’s relieved that his features have returned to normal and all traces of Galra are gone.

“Back with me?” he asks, brushing Keith’s sweaty bangs back from his forehead.

“Yeah,” says Keith shakily after a long moment. He suddenly looks acutely uncomfortable. “Look, I’m sorry for—”

“Don’t,” says Shiro, pressing a quick kiss to his lips. “You have nothing to apologise for.”

He pulls Keith on top of him so his head’s resting on his chest and continues stroking his hair. “Besides, at least this way we know what we’re in for. How long did Coran say these things usually last for?”

Keith fidgets a little before answering. “Five days,” he says, sounding apologetic.

“Oh,” says Shiro, keeping his voice carefully even, “great.”


End file.
